Metalized Flexible Vent for Bathroom

[John H. Cooper]

Gentlemen,

I wonder if you could help me out with this one. I have been advised that flexible plastic vent ducting is not allowed from bathroom vents. It could allow a fire to escape into the attic. Please see the attached photos.

In this case, metal ducting was used almost to the wall, but metalized flex duct, the slinky kind, was used between the solid ductwork and the wall, as well as from the fan unit to the solid duct work. In addition they used aluminum tape to seal all the joints in the solid ducting, but used "Duct Tape" to finish the connections.

What say you?

[Charley L. Bottger]

My response would be depends on your local AHJ mine allows flex to be used.

[Greg Veal]

Standard in my area as well. Basically uninsulated flexduct liner. Plastic or mylar type flexduct liners are not acceptable in our area.
Also, gray "fabric" duct tape is not acceptable, as used in your pic. Only smacna "foil" tape or rated Mastic is allowed.